how does a jetta act if the anti theif system has been actived

If nothing occurred after about an hour, it should show no signs. I think it has immobilization features for about an hour after the alarm goes off. Maybe someone else can pipe in on this.

If your anti-theft has been activated at first your horn and lights would have been going off at the same time it will lock out the ecm preventing starting the vehicle with or with out a key, you must deactivate the alarm with the remote (if equipped) if not using the ignition key in the drivers door lock turning it to the unlock position twice (sometimes only once) will deactivate the anti-theft.

Like the gentlemen before stated your alarm will sound and if they have tried to tamper with your car ignition the engine will not start.